DESCRIPTION: Optimism, or positive outcome expectancies, has been associated with better psychological and physical health, including changes in the immune system. Under moderately severe stress, optimists have more lymphocytes associated with cell-mediated immunity and natural killer cell cytotoxicity. The proposed research is intended to test whether optimism is beneficial during different sorts of stressors and using and in vivo measure of immune function. In a group of first year law students, optimism will be related to cell-mediated immunity, as measured by skin test over five time points: baseline (before school starts), a moderately severe stressor (mid-semester), a more sever stressor (final examinations), recovery (beginning of second semester) and feedback (return of first semester grades). The various time points allow for a test of the adaptiveness of optimism under different levels of stress and after confirmation or discontinuation of optimistic beliefs. Potential moderators and mediators of an optimism-immunity relationship will also be investigated. First, social network integration may provide a buffer; in its absence, optimism may be more important. Second, the degree to which optimism effects are independent of those of negative affectivity will be tested. Third, state positive and negative and cognitive appraisal processes may be psychosocial mediators by which optimism affects the immune system. The amount and rhythm of cortisol release is a potential physiological mediator. The results will have the potential to clarify the circumstances under which optimism is beneficial, differentiate optimisms effects from those of negative affectivity, and examine the role of mood, cognitive processes, and cortisol in stressor-related immune change. Given that interventions to increase optimism are being developed, it is becoming increasingly important to understand when and why optimism leads to better psychological health, less distress, and better immune function during stressors.